The drilling of the ground to make foundation piles with medium/low depth is diffusely carried out with the continuous flight auger technology. In order to carry out this technology self-propelled machines are usually used, which are equipped with a tracked truck and with a tower to which a guide tower is constrained, through an articulation. Such a guide tower in working conditions is kept substantially vertical or with small inclinations. On said tower a rotary head slides, which is known as “rotary” and which is equipped with a driving tube under which the digging auger is connected. The digging auger is made of a battery of digging elements until a length is reached that is substantially equal to the depth to be reached. The rotary head imparts rotary movement onto the auger, whereas the thrusting devices drive it into the ground. The two combined rotation and translation movements can produce a descent of the auger in the ground in order to dig a foundation hole. During digging, the rotation of the auger in combination with the inclination of the coils causes a rising of the digging debris along the coils until they are brought to the surface. Once the end of excavation depth has been reached, the auger is progressively extracted from the ground, thanks to the lifting movement of the rotary head along the antenna, and at the same time it can also be kept in rotation. During this step the auger is therefore subjected to a torque and to a “pull” of external forces that generate a traction sufficient to overcome the weight of the auger itself, the weight of the ground on the coils and the friction that is generated between the coil and the walls of the excavation. Generally the coils have a hollow core so as to make a duct inside the auger and at the end of the excavation. In this way, it is possible to pump setting material from the outside through the core of the auger in order to fill the excavation during the lifting step thus obtaining the foundation pile. The auger is generally made of a lower bit and multiple auger elements or segments that are axially connected to one another in order to make up the auger of the desired length. Based on the depth intended to be reached and on the performance allowed by the machine, the number of auger segments to be used to make up the digging auger is chosen. The auger segments, but also the bits, generally consist of a central cylindrical shaft and of coils that wind around the shaft. The shaft mainly consists of a hollow tube of great thickness, which is equipped at its ends with connection elements or joints and which must have sufficient diameter and thickness so as to withstand the pushing and pulling forces and the torques that the rotary head transmits to the auger during the excavation step. The coils consist of flat metal sheets properly folded and inclined in order to wind around the shaft. The outer diameter of the coils determines the actual diameter of the excavation made. The auger segments have lengths limited generally to values comprised between 2 m and 12 m, such as to promote the transportation thereof, thus limiting the weight and bulk thereof. The diameters of the coils, on the other hand, are limited based on the powers and on the torques that can be delivered by the rotary heads of the machines on which they must be mounted.
An alternative technique for making foundation piles, applicable in suitable grounds, is that of compaction of the ground. In this case, using the same digging machine described, a battery of compacting rods, also called excavation battery, at the base of which a compacting tool is applied, is applied to the rotary head instead of the auger. Also in this case, the excavation battery and the tool are made to penetrate into the ground through pushing and rotation, but in this case there is no removal of ground. The ground is just moved and compressed laterally towards the walls of the hole being made, without carrying the debris to the surface. The compacting rod elements are comparable to an auger element without external coils and are therefore “smooth” on the outside, i.e. they have a constant circular section. Such elements thus consist of a cylindrical shaft, which is mainly made of a hollow tube of great thickness, equipped at its ends with connection elements or joints, and which must have sufficient diameter and thickness so as to withstand the pushing and pulling forces and the torques that the rotary head transmits to the compacting tool during the excavation and lifting step. These rods as well are equipped with an inner duct that allows the passage of cement and therefore allows carrying out casting at the end of excavation and for the entire lifting from the bottom of the excavation.
In recent years, the increased power installed on the drilling machines, and therefore their increased performance, has led to a consequent increase in size of augers and rods that can be used. Currently, it is not rarely required to carry out foundation piles with diameter of 1,200 mm for a depth that tends to reach 30 m. For such great excavation depths, the composition of a drilling battery can thus require joining in situ four, five or more auger or rod segments.
Due to the great torques delivered by modern machines, the use of male-female threaded joints to carry out the mutual connection of the digging auger or smooth compacting rod segments has now been abandoned. In fact, such a threaded connection has not proven to be sufficiently strong. For some years it has thus been opted to join through male and female joints with prismatic section, for example square or hexagonal, capable of transmitting high torques, whereas the locking of the axial movement, in extraction, between two adjacent pieces is entrusted to transverse pegs and/or pins, of increasingly great size, in order to withstand the forces of the extraction members (winches, cylinders) that have also increased in line with the weight of the machines. Each auger segment has a male joint at one end and a female joint at the other end. The bit, on the other hand, has a single joint, which could be either male or female depending on the cases, positioned at the opposite end with respect to the digging direction. In this way, the male joint of an auger segment can be inserted axially into the female joint of the adjacent segment to make up the auger. Between the female joint and the male joint a coupling of the prismatic type is thus made, which prevents relative rotations of the two segments with respect to the longitudinal axis of the excavation battery that coincides with the rotation axis of the auger or of the rod during digging. Thanks to the fact that relative rotations are impossible, when an auger segment receives torque and is set in rotation it transmits such a torque and such a rotation to the connected adjacent segments. The male joint can consist of a shaft section of limited axial length, for example equal to one or two times the diameter of the shaft, equipped with outer faces arranged to form a polygon, preferably a square or a hexagon. Such a polygonal shape is visible by observing the auger along its axial dimension or by sectioning the joint with a plane perpendicular to the longitudinal axis of the auger. The size of this polygonal section is preferably less than the outer diameter of the shaft of the auger. The female joint, on the other hand, can consist of a shaft section of length at least equal to the male joint with outer diameter equal to that of the shaft and comprising a polygonal-shaped inner recess corresponding to that of the male joint. The recess will have dimensions with slightly greater tolerances with respect to the male in order to allow an easier axial insertion of the male joint into the female joint. The male joints and the female joints will also have transverse recesses, preferably with circular section, with axis arranged perpendicularly with respect to the axis of the auger, in order to allow the insertion of locking pins or pegs. Once inserted, each pin is in contact both with the male joint and with the female joint, thus preventing a relative axial sliding thereof in the direction of the longitudinal axis of the auger. The pins thus support the load of axial pull applied to the auger during the extraction step from the ground.
The prior art just described has some drawbacks.
At the start of the worksite, before making the excavation for the first pile, it is necessary to “make up” the excavation battery by assembling to one another some digging, auger or rod segments, until the desired length functional to the depth of the excavation is reached. Such segments are in fact stored on the worksite in mutually disconnected configuration, in order to limit the bulk thereof and to facilitate the movement thereof. The auger segments, or the rod, are assembled to one another under the rotary head at the tower of the machine to then connect the final rod or auger to the rotary head itself.
The known digging machine is, therefore, equipped with lifting means that favour the lifting and assembly maneuvers of the digging segments. Typically, the lifting means comprise a service winch equipped with a cable that is sent to pulleys arranged on the top of the guide tower and is then made to descend to the plane of the ground to be able to hook the segments to be lifted. Even in the case in which these lifting means are available to lift the auger or rod segments and to connect them to one another by engaging the respective male and female joints, it is still necessary to have an aerial service platform through which the upper part of the piece of segment that is wished to be added or removed, arranged vertically under the rotary head, must be reached, in order to insert the pegs or pins that connect said segment to the lower end of the battery that is already partially made up. Such an operation is to be repeated for each new segment added or subtracted and for the respective jointed connection. This insertion maneuver is carried out manually by trained workers operating, therefore, from an aerial platform that sometimes must reach 6-12 meters in height, based on the length of the auger segments that are coupled or based on the total length of the auger that is wished to be obtained. This maneuver, since it is carried out at a height, always involves a certain risk and requires the use of machinery, the aerial platform, distinct from the digging machine. The use of the platform also increases the worksite costs and can be difficult in worksites with limited space that reduces accessibility of the platform near the digging machine.
An alternative solution to the use of the aerial platform, in order to facilitate the composition of a battery of augers, is to use a “service well”, i.e. an excavation made previously in the ground and emptied of the excavated earth. Such an excavation, therefore, must have a greater diameter and depth with respect to the battery of augers or rods to be made up. For example, if it is necessary to mount a bit that is two meters long with two auger segments that are each six meters long, in the presence of a service well it is possible to follow the following procedure:    a) arranging the bit inside the mouth of the well, fixing it axially to the mouth of the well itself so that its upper end, usually equipped with female half-joint, projects slightly from the ground. A typical locking or sustaining method is to insert bars of greater diameter with respect to the well between the coils, so that they also rest beyond the edges of the mouth, thus preventing them from falling into it;    b) positioning the first six-meter auger segment in raised position above the bit, through the service winch of the machine itself or through an external crane. As known, it is necessary to angularly phase the two joints of the segments to be connected to then lower the auger segment so that the male joint inserts axially into the female one and then the bit and the adjacent segment are fixed axially through the insertion of the transverse pegs. The insertion of the locking pegs can thus be carried out by workers on the ground, since the joint is at a low height with respect to the ground;    c) through the service winch of the machine or by means of an external crane, the battery partially formed by the two assembled segments is lowered for further six meters into the well, locking it on the mouth of the well as soon as the upper joint of the first six-meter segment is at a lower height with respect to the plane of the ground;    d) positioning the second six-meter segment raised above the previous one through the service winch of the machine itself or external crane. Like previously, at this point it is necessary to angularly phase the two joints before lowering the auger segment so that the male joint inserts axially into the female one and then the segments are fixed axially through the insertion of the transverse pegs;    e) through the service winch of the machine or by means of an external crane the entirely made up battery of auger segments is lowered for another six meters into the well and it is locked on the mouth when only the upper joint of the second 6m-segment extends beyond the edge of the well;    f) moving the rotary head and the driving tube associated with it down along the guide antenna until the lower joint of the driving tube is inserted axially into the upper joint of the second six-meter segment. Then the transverse pegs or pins are inserted to axially lock the auger to the tube and therefore to the rotary head.
At this point the auger, made of a battery of assembled segments, is ready for use and is fixed securely to the rotary head. Then the auger is completely extracted from the well, completely lifting the rotary head along the guide tower, and the machine is moved inside the worksite until the position of the first pile to be made is reached.
The service well, in brief, allows always fixing the pegs close to the landscape plane, thus allowing the operation to be carried out by workers who keep their feet on the ground, thus without the aid of lifts.
However, the presence of a service well still remains a rarity due to some drawbacks, in particular due to the fact that the well is in a fixed point of the worksite, whereas the digging machines will work at many points and possibly with augers of different diameter according to the areas of the worksite. This involves that the machine, in order to carry out a change of augers, for example to modify the length or diameter thereof, will have to travel through the worksite to reach the well, where to make the change, and then return to the excavation area. This operation is complicated particularly in urban worksites with restricted spaces and, in any case, requires a long time due to the extremely low movement speeds of these digging machines. Moreover, the presence of a well on the worksite represents a danger, since in the case of a person accidentally falling the diameter of the well would allow the body to pass to the maximum depth. It is therefore clear that it is necessary to keep the well always covered and to cordon off the surrounding area when it is not in use.
In light of the problems linked to the service well, the procedure that is currently most frequently carried out on the worksite is as follows, which does not provide for the use of such a well.    a) Raising the rotary head until a raised position is reached along the guide antenna. By using the service winch, or an external crane, the bit of the excavation battery, which commonly is about two meters long, is arranged below the rotary table so that the longitudinal axis of the bit coincides as much as possible with the axis of the driving tube of the rotary head. Keeping the bit in a substantially vertical position possibly takes place by closing around it the openable guides with which a machine for continuous flight auger is generally equipped. These guides consist of two movable half-shells, constrained to the base of the guide tower, which can open or close by rotating on the horizontal plane to clutch or free the auger.    b) Lowering the rotary head and, after having angularly phased the lower joint of the tube with the upper joint of the auger segment, the two joints are engaged by making them slide axially inside one another. An operator climbs up a suitable ladder so that his/her hands reach the height at which the upper joint of the bit segment is located, generally two meters, and provides for engaging the transverse pegs that connect the digging segment with the tube of the rotary head.    c) By actuating the rotary head in rotation and in translation downwards, torque and thrust are applied to the segment until it is planted in the ground for about three quarters of its length.    d) The transverse pegs between the bit segment and the driving tube of the rotary head are extracted and the free rotary head is raised again to a height such as to free a space above the bit segment that is greater than the length of the next auger segment, for example six meters, which will be loaded to make up the auger.    e) Then the auger segment is lifted with the service winch of the machine, or with an external crane, and it is placed on the vertical of the bit segment planted in the ground. The lower joint of the auger segment is phased with the upper joint of the bit segment, the joints are engaged and the radial pegs are inserted.    f) With an aerial support platform for the operator that must be available on the worksite, a sufficient height is ascended to so as to insert the transverse pegs between the upper joint, generally female, of the segment just added and the lower joint of the driving tube of the rotary head. The platform, or basket, which carries the operator must therefore always reach a height at least equal to, but generally greater than, the length of the auger segment that is added, therefore, at heights that frequently exceed 6 meters, but could even reach 12 meters.    g) Once the joints have been secured with the pegs, torque and thrust are applied to the partially made up battery of augers until it is almost completely planted into the ground taking care to leave about a meter thereof, or in any case at least the entire upper joint, above the plane of the ground.    h) The fixing of the second six-meter digging segment on the first is carried out in the same way used to assemble the first auger segment on the bit segment.
The “elevated” intervention becomes necessary whenever an auger segment is added to the existing ones. The height depends on the length of the segment to be joined. The current safety standards in any case mandate the use of a service platform and of safety and protection devices for working at a height.
The operations are repeated for all of the successive auger segments that are wished to be added. The “elevated” intervention becomes necessary whenever an auger segment is added to the existing ones. In the absence of a service well and without the aid of accessories suitable for the purpose, it will always be necessary to have an elevator platform with which to raise workers to a few meters in height from the landscape plane to arrange the fixing of the transverse pegs that connect two adjacent auger segments to one another or that connect a segment to the tube of the rotary. The work is not simple since the workers need to drive in, or extract, pegs with a diameter of a few centimeters in seats having very precise tolerances that are necessary to eliminate the clearances, but that at the same time increase the friction and make the insertion difficult. Moreover, such insertions or extractions of the pins are carried out by worksite workers with a club, mallet, or ram thus requiring physical effort and exposure to the dangers deriving from the use of these clubs. The work position as well is not comfortable since the insertion maneuvers of the pins require that the shaft of the auger be reached, but at the same time the basket, or the platform, can approach only until reaching the outer edge of the coils. In the case of augers with coils of large diameter, the basket will thus be further from the shaft, requiring the operator to lean out and work in an uncomfortable position.